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United States Patent | 6,166,922 |
Kobori ,   et al. | December 26, 2000 |
A current detecting circuit detects amplitude of a current flowing toward the connecting point of a first transistor and a serial circuit through a second transistor and a comparing circuit compares amplitude of the current detected by the current detecting circuit with the reference value. An oscillation control circuit controls a control current supplied to an oscillating circuit in order to raise the oscillation frequency of the oscillating circuit when amplitude of the current detected by the current detecting circuit is smaller than the reference value as a result of comparison by the comparing circuit in view of preventing the oscillation frequency to be further lowered. Therefore, it is no longer required to design the apparatus by giving allowance to take into consideration the temperature characteristics and fluctuation of parts unlike the related art in which the minimum oscillation frequency of the oscillating circuit is set. Accordingly, variable range of the oscillation frequency can be expanded. As a result, it can be prevented that variable range of the oscillation frequency of the oscillating circuit becomes narrower.
Inventors: | Kobori; Makoto (Miyagi, JP); Kaneko; Susumu (Miyagi, JP) |
Assignee: | Sony Corporation (Tokyo, JP) |
Appl. No.: | 426342 |
Filed: | October 25, 1999 |
Oct 26, 1998[JP] | 10-304376 |
Current U.S. Class: | 363/17; 363/25; 363/97 |
Intern'l Class: | H02M 003/335; H02M 003/24; H02M 005/42 |
Field of Search: | 363/17,132,16,24,25,55,56,95,97,131,134 |
5321235 | Jun., 1994 | Makino et al. | 363/98. |
5719755 | Feb., 1998 | Usui | 363/19. |
5748458 | May., 1998 | Ochiai | 363/17. |
5965989 | Oct., 1999 | Mader | 363/25. |
6021052 | Feb., 2000 | Unger et al. | 363/26. |
6038142 | Mar., 2000 | Fraidlin et al. | 363/17. |